Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.115: Poster

Tuesday, March 27, 2007, 15:00–19:00, Poster A

Evolution of magnetization from the vortex state in soft magnetic square platelets — Manfred Wolf, •Ulrich K. Rößler, and Rudolf Schäfer — IFW Dresden

The zero-field ground state of magnetically soft films (with lateral dimensions above the single-domain limit) is governed by the demagnetization energy, which causes flux-closure. The quasistatic magnetization process in an external field is obtained by minimizing the micromagnetic free energy. Much like domains, the magnetization patterns in these structures are determined by the sample geometry and the applied field H. These patterns can display regions with homogeneous magnetization separated by walls and can be understood with a scaling analysis of the different energy contributions in the micromagnetic energy, which is valid for films of vanishing thickness t → 0.

Here we investigate the magnetization process and the evolution of the vortex pattern in square Permalloy platelets with edge lengths l=1 µm and finite t = 8, 12, 16 and 20 nm and for a field applied along the square’s diagonal by numerical computation using a standard micromagnetism code. The results can be semi-quantitatively understood by a modified phase theory approximation that describes the magnetization process in terms of the position of the vortex as single parameter. This approach gives a good explanation, as a function of the film thickness, of (i) the critical field, at which the vortex is expelled, (ii) the initial slope of the magnetization-vs-field curve m(H), (iii) the dependence of the field energy on m, and (iv) the dependence of the demagnetization energy.